This invention relates to porous ceramic articles or structures for use as molten metal filters, traps for particulates in exhaust gases such as Diesel engine exhaust gases, other filters, catalyst carriers, energy-saving members such as gas-permeable thermal insulators or the like, particularly at elevated temperatures.
Porous ceramic bodies are prepared by applying a ceramic slurry to an open-cell synthetic resin foam such as reticulated or cell membrance-free flexible polyurethane foam, and drying and sintering the treated foam. They are advantageously used as filters and energy-saving members at elevated temperatures, for example, as filters for removing metal oxides in molten metal such as molten aluminum and trapping particulates in exhaust gases such as Diesel engine exhaust gases, and as gas-permeable thermal insulators or solid heat-transfer transducers to be mounted in a radiant tube or at a heated-gas outlet of a heating furnace to make use of the radiant heat of the gas.
While such a porous ceramic body is used at elevated temperatures, it will possibly be broken because of thermal shock or thermal stress. To increase the resistance of a porous ceramic body to thermal shock due to abrupt temperature changes or thermal stress due to uneven temperature, porous ceramic bodies are formed to have a reduced coefficient of thermal expansion so that stress occurrence is minimized. There is, however, the need for further improving thermal properties such as thermal shock resistance and heat resistance.
Since in such applications, porous ceramic bodies are often exposed to an extremely high temperature environment ranging from several hundred degrees to one thousand degrees centigrade, they are also required to have increased strength at such extremely high temperatures. Preferably the porous ceramic bodies are formed of alumina or cordierite as a main ingredient to achieve such high-temperature strength. There is the need for porous ceramic bodies having further improved high-temperature strength.